M32 Engine

The M32 engine (Figure 21.2) superseded the well-established M453C series, a 320 mm bore/420 mm stroke design which had been offered as an in-line engine with six, eight and nine cylinders or as V12 and V16 versions with an output per cylinder of 370 kW. A substantial increase in power was yielded by the 320 mm bore M32 design whose modular construction also achieved an engine with 40 per cent fewer parts than its predecessor.

The in-line six-, eight- and nine-cylinder M32 models have a 480 mm stroke and originally yielded an output per cylinder of 440 kW at 600 rev/min, covering an output band from 2400 kW to 3960 kW at the economic continuous rating (ECR). The rating was raised to 480 kW/cylinder in 1998 to meet market requirements. V-configuration

Figure 21.2 Upper part of M32 engine

models (12 and 16 cylinders) introduced in 1997 retained the 420 mm stroke of the M453C design and offered up to 480 kW per cylinder at 750 rev/min. The ECR outputs of the V-versions range from 4800 kW to 7700 kW.

The designer highlights the following key features of the in-line cylinder M32 models which mainly target marine applications:

• Optimum thermodynamic conditions: a stroke/bore ratio of 1.5 promotes a favourable air/fuel mixture and combustion in a spacious combustion chamber. Simultaneously, a high compression ratio (14.5:1) fosters low fuel consumption—around 180 g/kWh at full load—and low noxious exhaust emission values.

• Integral construction: advanced machining centres allow components to be fashioned to serve several functions. The engine frame, for example, embodies cast-on boxes for the camshaft drive on the flywheel end, and the vibration damper and secondary pinion gear for auxiliaries on the free end. The frame also conveys the charge air to the cylinders via a cast-in duct. The camshaft runs directly in the frame.

• Stiff backbone: the integral engine frame permits the firing and mass forces to flow through the frame, matching the flux of the lines of force and with low deformation. Girder-like cross-sections run through the engine housing in a longitudinal direction yielding, together with stiff walls, a system with high bending and torsional rigidity. Rigid as well as resilient foundation work is easily effected, and structure- and air-borne sound emissions are kept at a low level.

The 'supporting' and 'cooling' functions are clearly separated in the engine frame which is immune from any corrosion damage because no cooling water flows within it. The cylinder liner, however, is cooled where it is most important: in the upper region outside the engine frame.

• Robust running gear: the train from piston to crankshaft is designed for a high load-carrying capacity to secure operational reliability and provide reserves for future development in line with market demands. The integral construction ensures a safe bedding for the crankshaft, camshaft, camshaft drive and cam followers, fostering long service life values (Figure 21.3).

• Modular system: the integrated sub-assemblies, such as the cylinder head and engine frame, are complemented by support system modules designed with a reduced number of components for easy pre-assembly and flexibility of application. An example is provided by the modular turbocharging package whose charge air cooler is housed drawer-like in a console screwed onto the frame (Figure 21.4).

• Functional groupings: arranged to facilitate operation and maintenance procedures. The camshaft side of the engine is easily accessible because there are no obstructions from charge air ducts and other mountings. The exhaust gas pipes are arranged on the opposite side. An optimized flow in the cylinder head ensures low flow coefficients in the tandem conduits for the inlet air and the exhaust gas. Simplified maintenance was addressed by specifying plugin type connections throughout, with special tools only required where conventional tools could not guarantee an adequate degree of mounting security.

A six-element hydraulic tool is used to release simultaneously the six nuts securing the cylinder head studs (Figure 21.5). A single bolt tightens the clamped joint between the cylinder head and the exhaust

Figure 21.3 M32 crankshaft installation
Figure 21.4 The M32 engine's charge air cooler is housed drawer-like in a console screwed onto the frame
Figure 21.5 A six-element hydraulic tool is used to secure or release the M32 cylinder head nuts

gas pipe. The fuel injection pump and nozzle can be disconnected by releasing just one screwed connection.

The connecting rod (Figure 21.6) is split just below the lower edge of the piston, promoting a low removal height for the running gear. The bearings do not have to be opened when a piston is drawn.

• Tough materials: essential castings, such as the engine frame and cylinder head, derive stiffness and security against fracture from high tensile nodular cast iron structures. The material inhibits elastic movement of the frame when subjected to firing forces. The circularity of the liners and the bedding of the plain bearings thus remain virtually unaffected and the axes of the gearwheels are maintained in parallel.

The material stiffness and stable design of the cylinder head secure a firm seating for the valves (Figure 21.7). The high Young's modulus of the nodular cast iron, the thick combustion chamber bottom and the adjacent cooling bores combine to foster operational reliability from the chamber and valves. The piston skirt is also of nodular cast iron, while the steel crown is served by numerous cooling bores.

Figure 21.6 The connecting rod of the M32 engine is split just below the lower edge of the piston
Figure 21.7 M32 cylinder head

• Low thermal load: the measured exhaust valve temperature of 390°C means that the Colmonoy armouring of the valves is highly resistant to inter-metallic corrosion attacks. A temperature of below 300°C measured on the outside of the piston crown permits only soft deposits.

Fuel injection can be adjusted for commencement, duration and pressure. Specially shaped control edges on the injection pump plunger secure correct commencement of injection as a function of output and speed. The M32 engine can also be provided with eccentric control of the cam follower between the camshaft and the injection pump. This arrangement facilitates simple adjustment of the firing pressure to suit the particular fuel grade or the climatic conditions and achieve optimum economy and operation on heavy fuel. Control of injection pressure is effected by an MaK-patented system which is said to foster part-load running with particularly low emissions and to enhance the ignition of heavy fuels.

Conventional injection pump systems deliver fuel in pulses which can cause vibrations in the associated piping and damage to upstream systems. The M32 engine features a system based on larger volumes with intermediate throttles for damping the delivery process without restraining it. The remaining vibrations in the fuel admission and return pipes are reportedly so low that elastic transition elements can be fitted between the pumps.

Adjustable valve timing is also required for special operating modes or to influence emission behaviour. The pushrods for the inlet and exhaust valves are therefore arranged on cam followers which can be adjusted by an optional eccentric. This arrangement reportedly allows valve overlap and the turbocharging group characteristic to be adapted to secure good part-load performance.

Like its predecessors, the M32 design is served by a pulse charging system allowing permanent operation on the propeller curve. As an option for particularly difficult applications, the in-line engine can be specified with control of the turbocharger turbine surface by MaK's Variable Multi Pulse (VMP) system. Faster acceleration, lower temperatures and higher part-load torques are possible. The designer has also developed systems for air bypass, exhaust gas blow-off and air blow-off.

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